The invention relates to a procedure for the reprocessing of used lubricating oils by treating dried oil with finely dispersed sodium metal at elevated temperature and subsequent separation of the processed product by distillation.
The reprocessing of use lubricating oils is a problem of increasing economic and ecological importance. Hitherto, this regeneration has been carried out predominantly in accordance with the so-called acid tar process, whereby the predried, old oils from which the benzine has been extracted, are subjected to a treatment with 5 to 15% of concentrated sulfuric acid and the treated product is subsequently decolored with heat using 3 to 10% of bleaching clay.
This process is usable per se, however, it is imbued with a few serious disadvantages. For one thing, the acid oils and the acid residues lead to considerable undesirable odors in the vicinity of the processing installations. For another thing, the considerable quantities of waste in the form of acid tar as well as of the bleaching clay filter cake, likewise represent a considerable ecological problem.
Therefore, the art has been searching for some other process which would lead in an economical manner to high grade, secondary raffinates, ecologically justifiable at the same time and producing as little waste material as possible.
Thus, an entire series of processes have previously been proposed in the case of which a generally large part of the inpurities contained is separated even before the acidification by additional chemical and physical treatment of the used oils, in order to decrease the amount of sulfuric acid needed for the oil and thus to produce smaller qualities of the undersirable acid tar. After that, the used oils are to be subjected, for example, to a solvent extraction prior to the acid treatment, a total evaporation, possibly with the addition of substances with alkaline reaction, to a coagulation by means of hydroxides of multivalent metals or to a hot treatment.
However, all these processes have not yet brought about a decisive breakthrough away from the classic acid tar process, for the reasons that the additional processing steps adversely affect the economy of the process; a further waste product is produced and because the waste producing steps of the acidification and treatment with bleaching clay must be carried out just as before with filtration.
Processes which operate entirely without acid treatment have also been previously described. In most cases, these known methods are combination of distillation, hydrogenation and filtration. The catalytic hydrogenation which otherwise plays a predominant role in the case of refining of hydrocarbons, is however less suitable in the case of the regeneration of used oils for two reasons: lubricating oil additives and their decomposition products as well as a halogen content that can never be excluded entirely, act as catalyst poisons and require a more or less expensive prepurification of the oils, for example, by total evaporation or solvent extraction. Beyond that, the necessary hydrogen is not economically available in the case of most medium size enterprises.
Two additional processes, described in the German Pat. No. 11 05 543 and the German OS No. 25 08 713 carry out a chemical treatment with sodium metal, but also only partially avoid the above mentioned disadvantages.
A variation according to the practice of the process described in the German Pat. No. 11 05 543 provides for the treatment in the presence of bleaching clay of a used oil regenerate obtained according to the sulfuric acid process with about 1.5% by weight of sodium metal dispersed in the regenerate and then to filter off the treatment product by way of additional bleaching clay. This process, however, is expensive because of the cost for the sodium metal and the bleaching clay and also was not able to gain grounds because of the difficulties encountered with the filtration of alkaline oils, particularly because of the high content of additives in today's lubricating oils, the requirement for auxiliary agents for filtering would have to be increased by a multiple of the originally provided volume with an unfavorable effect on the waste balance.
Another process described in the German OS No. 25 08 713 for the reprocessing of used mineral oil provides for the precleaning of the used oil by means of coagulation, adsorption, filtration as well as distillation and secondary treatment and to dehalogenize it subsequently in sequence, to distill it in a fractionated manner and to dehydrate it. For the dehalogenation, among others, a treatment with alkali metal in a volume rate of 1 to 2000 mole/1000 kilograms with exclusion of air and moisture at a reaction temperature of 15 to 300.degree. C. is proposed. Excess treatment agents and the reaction products formed should be separated either by distillation or by a cleaning treatment of the oil. In the first case, excess agent is allowed to deposit, the oil is decanted and is then distilled in the vacuum. In the second case, excess agent is destroyed with water, the oil is then cleaned with a diluted sulfuric acid and subsequently several times with water, is dried and filtered. Both alternatives are followed by the catalytic hydrogenation.
The large number of treatment steps alone is an impediment to an economic execution of this process. If one limits the observation to the step of the dehalogenation and the separation of oil and excess of processing agents, as well as to reaction products formed by decanting and distilling, then the last mentioned measure is made a great deal more difficult through the so-called "gum-formation," a resinification of the oil occurring in the case of all used oil treatment processes with alkali metal. This resinification is the more extensive, the higher the added quantity of the alkali metal and the higher the treatment temperature. Thus, for example, in the case of a distillation of oils treated at 100.degree. to 250.degree. C. with 1 to 2% by weight of sodium metal in the wetted wall distillation process, such strong spraying occurs that a double total evaporation may not be avoided and one must put up with a poorly distilled out residue of considerable volume.
If on the other hand, the processing of the oil from the dehalogenation stage by filtration is selected, then this presupposes the very expensive washing and drying process described.